Drill string stabilizers are commonly used on the steel tubes which carry a drill bit for boring into rocks or the ground or the like. The stabilizers are essentially enlargements which provide a limited surface radially outwardly of the drill supporting tube in order to center the drill string and the drill bit within the bore.
By way of example, bits for drilling through rock are frequently designed to rotate about their own centers so that centering the bits within the bore is necessary in order to insure designed or specified penetration rates as well as to reduce dulling or excess wear upon the bits. In order to maintain concentricity, the drill is centered by means of enlargements formed upon the tubes which support the drill. The enlargements must be radially accurately formed in dimension and preferably maintained at the same radius as is the bit itself in order to guide the bit along the center of the bore. Without stabilization, the drill tubes may move out of concentricity or chatter or bump along the bore walls thereby increasing wear on the bit as well as reducing its efficiency of operation.
Hence, stabilizers are frequently used in drilling deep bores, such as for oil wells, gas wells, as well as for blasting openings and the like.
Although various types of stabilizers are used, one commonly used form comprises raised ribs welded along the drill string sections with these ribs either being straight and aligned with the longitudinal axis of the drill tube or alternatively, spiraled about the tube surface. These rib-type stabilizers are initially made to conform to the radius of the drill and their outside surfaces rub against or otherwise contact the bore walls to maintain concentricity of the string of tubes which support the drill. Such stabilizers may be formed at various spaced apart locations along the drill tube string from the drill bit itself upwardly toward the outer surface of the bore.
Because the exposed surfaces of the rib-type stabilizers drag and scrape and otherwise rub against the bore wall which may comprise either the rock formation or alternatively well casing tubes, there is considerable abrasion which wears the stabilizers rapidly and thus, witin a relatively short period of time, ruins the accuracy of the radial dimensions of the stabilizer surfaces. A number of techniques have been developed in order to reduce the amount of wear or at least to slow it down for longer use of the drill string before replacement of the stabilizers.
One method of increasing the wear resistance of the stabilizer has been to coat the exposed surfaces with tungsten carbide particles brazed thereon so as to resist the abrasion of the bore wall. Thus, the invention herein relates to certain improvements in that type of wear resistant coating.
The present method of forming a carbide type wear resistant coating on rib-type stabilizers is a relatively expensive and time consuming operation. The first step involves preparing the exposed or outer surface of the stabilizers which are formed on a short tube section, to receive carbide. That is, the surfaces of the stabilizer must be suitably cleaned, etc., and then carbide particles in steel tubes or braze metal are gas or arc torch welded or brazed to the surface of a stabilizer. Little by little, along each stabilizer surface, carbide is added through this welding or brazing process and then the layer is built up to required thickness. After each of the stabilizers are appropriately coated with layers of suitable thickness, the tube may then be hand ground to size or may be placed in a grinding machine where it is rotated against a grinding wheel to produce a peripheral surface of the required radius.
This is a slow procedure, involving at least several hours of hand brazing, plus grinding and cleaning and the like which is relatively expensive. The procedure ordinarily must be carried out within a suitable factory having the equipment available and the atmosphere within which brazing may be conducted. Thus, when the carbide hard face stabilizer surface becomes worn so that it is no longer dimensionally acceptable, the stabilizer tube section is normally removed from the drill string and the section is shipped to a factory for re-processing, i.e., cleaning up and re-surfacing and heat treating for stress relief, etc. This is not the kind of procedure that can be carried out in the field ordinarily. When done in the field, the accuracy is subject to the skill of the individual mechanic so that the results are unreliable.
A particular problem involved in this method of hard surfacing, which at times has been done by attempting to melt and adhere upon the surface a mixture of binder or brazing material and carbide supplied in a rod-like form, is the fact that the completed surface is very rough and accurate dimensions cannot be obtained without the final step of grinding. Even there, the grinding does not always produce a good smooth surface and in addition, the fact that the grinding is carried out against hard carbide, results in the rapid wearing out of expensive grinding wheels.
Hence, the invention herein is concerned with hard surfacing the stabilizer surfaces rapidly, inexpensively, with minimal equipment and in a way that the job can be carried out in the field where the oil wells are located or where other types of drilling operations are performed.